Adds service files into the Debian package

Adds systemd unit and SysV init script for a system-wide Onionprobe service using /etc/onionprobe/onionprobe.yaml.

By default the service is not enabled, since Onionprobe should not be opinionated about how the user wants to run it -- whether as a standalone tool or a service.

It's currently passing lintian without errors or warnings, but still needs testing.

Main issue: Onionprobe: Debian package.

configs/onionprobe.yaml

+---
+# Onionprobe default system-wide service configuration.
+#
+# Edit this file according to the examples provided in this folder,
+# as by default it does not do much besides looping into the default
+# Onion Service to be tested, which is The Tor Project website.
+
+# Whether to run continuously
+loop: true